The problem of poor indoor air quality is found to be the cause of many health hazards, especially in modern domestic and commercial buildings where volatile organic compounds, nitrous oxide, ozone, and etc. are released by interior furnishing material as well as by human activities. Ventilation is not necessarily an adequate solution because outdoor air may be problematic as well. In addition, the energy load on the air-conditioning system is greater once outdoor air is used to ventilate the indoor space.
Common air-cleaners typically use activated carbon as a gas adsorbent. However, activated carbon filters tend to be expensive and must be periodically disposed of and replaced. The heterogeneously porous structure of activated carbon leads to competitive adsorption between water vapor and organic compounds, and eventually reduces its removal effectiveness. Moreover, heat generated from the adsorption process causes polymerization of the structure, and this degrading of the activated carbon structure further decreases the adsorption performance. Additionally, activate carbon is thermally unstable, high temperature regeneration is impractical and unsafe to do outside of a laboratory. As with most adsorption methods, the contaminant is not destroyed but merely transferred from the air onto the filter medium. This can lead to messy and dangerous cleaning processes. Prior inventions, such as that disclosed in U.S. Pat. No. 5,827,355, present a system with built-in regenerative processes of a carbon fiber composite molecular sieve by applying electrical currents to the filter medium. However, this process requires higher temperatures than those needed for zeolite regeneration. Additionally, the heating regeneration process periodically purges the filter of the contaminants and releases them back into the atmosphere. The present invention has the advantage of continuously decomposing the contaminant on the filter.
Photo-catalytic air-cleaners, such as that disclosed in U.S. Pat. No. 5,835,840, are also available and have the advantages of permanently removing the contaminants and having low maintenance and operating costs. However, when used unaccompanied by another device these systems are found to be slow acting and often produce imperceptible effects. U.S. Pat. No. 6,358,374 B1 discloses a system that integrates photo-catalytic technologies and adsorbent technologies. However, this system has a cumbersome method of periodically heating the adsorbent material, which releases a concentrated form of the contaminant into a chamber where the photo-catalytic mechanism is then applied. If there were a malfunctioning or leakage, it seems that this chamber of concentrated contaminants could become dangerous, depending on the type of contaminant contained within. Also, a substantial amount of contaminant must typically be absorbed before the system is regenerated. The preferred embodiment of the present invention has the advantage of being continuously self-regenerative without the use of the heater. In embodiments where the heater is employed the contaminants are decomposed during the heating process, unlike prior inventions. Additionally, in the present invention the contaminants remain secured on the zeolite until they are oxidized, a much less cumbersome and safer method.
Ion cluster emitting devices are also available, but have been found to act weakly on chemical pollutants. Charged ions clusters are generally effective in killing bacteria in the air, and decomposing certain odorous gases. However, an ion generator alone is ineffective in completely cleaning the air because the chance of charged ion cluster interacting with the contaminant gas molecule or bacteria is quite small. Moreover, charged ions clusters tend to react with the oxygen in the air to produce ozone, which in high concentrations is hazardous to human health. U.S. Pat. No. 5,702,507 discloses an invention that employs an ozone generator to destroy bacteria in the air. However, particularly in areas of low contaminant concentration, if the production of ozone is not carefully controlled, the growing levels of ozone could in fact create a worse indoor air quality level than that prior to employing the air cleaner. The present invention has the advantage of providing an inherent mechanism to eliminate the release of ozone.
Molecular sieves, such as zeolite or other crystalline zeolite complementary materials have a high porosity, and are effective in trapping contaminant gas molecules. Synthetic zeolite, unlike activated carbon, exhibits selectivity on adsorbed contaminants depending upon the shape, orientation, size hydrophilicity and chemical nature of the pores in zeolite. This allows specific filters to be developed to adsorb specific pollutants, increasing efficiency of an individual filter. Zeolite is also inexpensively produced, compared to activated carbon. Additionally, artificial zeolite production is environmentally friendly and takes advantage of unused resources, such as pyroclastic materials, inceration ash, waste glass, waste diatomaceous earth, and aluminum dross. A method for producing artificial zeolite is disclosed in U.S. Pat. No. 6,299,854 B1.
The thermal characteristics of zeolite make regeneration possible. At ambient temperatures, contaminant gas is adsorbed by zeolite because of the high porosity of zeolite crystallization and the weak polarity of zeolite molecules. When exposed to temperature above 45° C. temperature, the adsorbed gas molecules starting to release back to atmosphere. In a system where zeolite is used alone, without a regeneration device, the contaminants are merely secured until regeneration can occur. The contaminants are then released upon regeneration. The present invention is a system that takes advantage of zeolite's superior ability to adsorb pollutants, while also incorporating the technology of catalytic oxidation inside the pores of it.